Refrigeration system for cooling chips in test

ABSTRACT

An air cooling system including a first desiccant dryer, a second desiccant dryer connected in series in a flow path with the first desiccant dryer and a first air cooling unit connected in series in the flow path with the second desiccant dryer.

This application is a continuation of Ser. No. 09/345,334 filed Jul. 1,1999.

FIELD OF THE INVENTION

The invention relates to a method and apparatus for cooling electronicdevices, such as semiconductor chips, during testing of the devices.

BACKGROUND OF THE INVENTION

To test their operability and resistance to a variety of conditions,semiconductor chips are typically subjected to a variety of tests. Forexample, the chips may be cooled to test their resistance to subfreezingtemperatures. To carry out a test wherein a semiconductor chip isexposed to cold temperatures.

SUMMARY OF THE INVENTION

The present invention provides an air cooling system for utilization insemiconductor chip testing. The air cooling system includes a firstdesiccant dryer. A second dryer is connected in a series in a flow pathwith the first desiccant dryer. A first air cooling unit is connected inseries in the flow path with the second desiccant dryer.

The present invention also provides a method for cooling and drying air.The method includes drying the air such that it comprises about 4.5grains of moisture. The air is cooled to about 73° F. The air is furthercooled and dried such that the air includes less than about 4.5 grainsof moisture and is at a temperature of about −39° C. by passing the airover cooling fins cooled by a non-nitrogen based coolant.

Additionally, the present invention provides a method for cooling anddrying air. The method includes transmitting air through a firstdesiccant dryer. The air is then transmitted through a second desiccantdryer connected in a series in a flow path with the first desiccantdryer. Next, the air is transmitted through a first air cooling unitconnected in series in the flow path with the second desiccant dryer.

Furthermore, the present invention provides a method testing asemiconductor device. The method includes arranging the semiconductordevice on a testing apparatus. Air is transmitted through the firstdesiccant dryer. The air is then transmitted through a second desiccantdryer connected in series in a flow path with the first desiccant dryer.Subsequently, the air is transmitted through a first air cooling unitconnected in series in the flow path with the second desiccant dryer.Then, the air is directed to the testing device to cool thesemiconductor device.

Still further, the present invention provides a method for testing asemiconductor device. The method includes arranging the semiconductordevice on a testing apparatus. Air is dried such that includes about 4.5grains of moisture. The air is cooled to about 73° F. The air is furthercooled and dried such that the air includes less than about 4.5 grainsof moisture and is at a temperature of about −39° C. by passing the airover cooling fins cooled by non-nitrogen based coolant. Then, the air isdirected to at least one testing device to cool the semiconductordevice.

Still other objects and advantages of the present invention will becomereadily apparent by those skilled in the art from the following detaileddescription, wherein it is shown and described only the preferredembodiments of the invention, simply by way of illustration of the bestmode contemplated of carrying out the invention. As will be realized,the invention is capable of other and different embodiments, and itsseveral details are capable of modifications in various obviousrespects, without departing from the invention. Accordingly, thedrawings and description are to be regarded as illustrative in natureand not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned objects and advantages of the present invention willbe more clearly understood when considered in conjunction with theaccompanying drawings, in which:

FIG. 1 represents a schematic view of an embodiment of a deviceaccording to the present invention; and

FIG. 2 represents a cross-sectional schematic view of one embodiment ofan air cooling unit that may be utilized in a cooling system accordingto the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Electronic devices, such as semiconductor chips are routinely subjectedto tests to determine their operational characteristics and limits,among other things. As described above, one test that semiconductorchips are subjected to includes exposure to subfreezing temperatures totest operation of the chips under such conditions. Commonly, such tests,typically known as sub-cooling tests are performed on a number of chipsutilizing liquid nitrogen as the cooling agent to cool the air. Afterthe test, typically the air is quickly reheated, creating wastefuloperating costs, ice build up and possible hazards to personnel.

Currently, as well as in the past, cool air typically is produced byutilizing liquid nitrogen to chill air down to about −55° C. However,liquid nitrogen may freeze condensate in a test chamber. Liquid nitrogenmay be injected at −160° C. directly into a cooling chamber and thenevaporated and heated to about −10° C.

While this may be the least costly way to cool the air, at least fromthe perspective of an air handler company, it may result in a number ofproblems. For example, leaks may be created in plumbing, wire access,and gasket panels. The leaks may cause condensate to freeze in thechamber. Such an apparatus may also create a safety hazard due to watermelting from the chamber onto electrical components and the floor.

Additionally, such a system has a great cost for defrosting due to icebuild up. In some cases, an air cooling system must be defrosted every 8hours and can consume as much as two hours in extreme cases. Theseproblems may result in requiring additional testers and handlers to meetproduction requirements.

The present invention provides a solution to the above-describedproblems and others by providing a system that permits a fast turnaround to be carried out in switching from hot to cold air testingwithout a significant loss in manufacturing time due to equipmentfreeze-up typically encountered in processes that utilize liquidnitrogen. While overcoming these problems, the present invention stillmaintains the capability of sub-freezing temperature testing.

In short, the present invention provides an air cooling system thatincludes a first desiccant dryer. The system also includes a seconddesiccant dryer connected in series in a flow path with the firstdesiccant dryer. A first air cooling unit is connected in series in theflow path with the second desiccant dryer.

By including two desiccant dryers in series, a second dryer may belocated in a processor closer to where the air will be utilized ratherthan in a central location. This decreases the chance of moisturereentering the air stream. Additionally, locating a second dryer on acooling unit may occupy less space and also decrease the chance ofmoisture migration back into the system. This may at least in partbecause the air is cooled right after drying. This decreases the chanceof moisture seeping into the air prior to cooling. Including only onedryer may make a system according to the present invention too bigand/or too noisy.

While typical embodiments of the present invention include two desiccantdryers, the present invention may include any number of desiccantdryers. For example, a system according to the present invention mayinclude more than two desiccant dryers. Along these lines, a systemaccording to the present invention could include a plurality of seconddesiccant dryers. According to such embodiments, the first desiccantdryer may be in series with the plurality of second desiccant dryers.According to such an embodiment, air would flow from the first desiccantdryer along a plurality of different flow paths to each of the seconddesiccant dryers. Therefore, the plurality of second desiccant dryersmay be considered to be connected in parallel.

Any desiccant dryer may be included in the system according to thepresent invention. One specific example of a desiccant dryer is a silicagel desiccant dryer with electric heater available from Cargoair.

A system according to the present invention may also include a secondair cooling unit in series in the flow path between the first desiccantdryer and the second desiccant dryer. As with the desiccant dryers, thepresent invention may include any suitable air cooling unit. One exampleof a suitable air cooling unit is a PGC unit available from ParameterGeneration and Control, Inc. of Black Mountain, N.C.

While any air cooling unit may be utilized, the first and/or the secondair cooling unit may be dehumidifying. Additionally, either the firstand/or second air cooling unit may be a multi-stage cooling unit. Alongthese lines, either one or both of the air cooling units may include achilled water cooling coil. Additionally, the first air cooling unit mayinclude multiple stages of direct expansion coils.

A system according to the present invention may further include a thirdair cooling unit. A third air cooling could be arranged upstream fromand in series with the first desiccant dryer. Such a third air coolingunit would cool air before the air enters the first desiccant dryer.

While the air cooling units according to the present invention referredto as first, second and third, it is not necessary that a systemaccording to the present invention include more than one air coolingunit. Additionally, the at least one air cooling unit could be arrangedin any position in the system. For example, the at least one air coolingunit could be arranged an any position where the first, second and/orthird air cooling unit may be arranged as described herein. Of course, asystem according to the present invention could include two air coolingunits arranged in any position, such as two of the positions describedherein for an air cooling unit.

According to the present invention, the desiccant dryer(s) and aircooling unit(s) may be arranged in a variety of configurations. Alongthese lines, the desiccant dryer(s) and air cooling unit(s) may bearranged in close proximity to each other. According to one example, theair cooling system according to the present invention includes a seconddesiccant dryer arranged adjacent to a first air cooling unit. Accordingto a variation of this embodiment, the second desiccant dryer isintegrated with the first air cooling unit. According to anothervariation of this embodiment, the second desiccant dryer is arranged ontop of the first air cooling unit.

As is evident from this discussion, the desiccant dryer(s) and aircooling unit(s) may be arranged in any configuration relative to eachother. However, some configurations may provide particular advantages ascompared to others. For example, some embodiments, such as the onedescribed above where a desiccant dryer is arranged in the vicinity ofor as with the air cooling unit may provide an advantage of being morecompact then other embodiments.

The capacity of the system according to the present invention to removemoisture and cool air may vary depending upon the embodiment as well asthe desire characteristics of the air to be treated by the system.Typically, if a system according to the present invention includes afirst desiccant dryer and second desiccant dryer, the first desiccantdryer removes a first portion of moisture from air passing therethroughand the second desiccant dryer removes an additional portion of moisturefrom the air passing therethrough. The amount of moisture that eachdesiccant dryer removes from the air may vary depending upon theembodiment. According to one embodiment, air flowing out of the seconddesiccant dryer has a moisture content of less than 1 grain.

Significantly, it should be noted that the temperature, moisturecontent, flow rates, and other characteristics of air treated with asystem according to the present invention may vary, depending upon,among other factors, the temperature and moisture content of the inputair and the requirements for the end use of the air. Similarly, thecharacteristics of the air may vary at any point within a systemaccording to the present invention. For example, reference is madeherein to processing air such that at a first stage is has a moisturecontent of about 4.5 grains. this could be greater or lesser, dependingat least in part upon the properties of the air input into the system atinput 3.

After being treated by a system according to the present invention, airmay be directed toward to at least one process tool. A process tool maybe for the purpose of testing semiconductor chips. The air may also befor other processes. Along these lines, a testing apparatus thatutilizes air treated according to the present invention may notnecessarily be for treating a semiconductor chip. In fact, it can beutilized for testing other electronic components.

The relationship of the system according to the present inventionrelative to the process tool may vary. According to one embodiment, thesystem according to the present invention is remote from the processtool. According to other embodiments, the system according to thepresent invention is in close proximity to the process tool.

According to some embodiments, one or more elements of a systemaccording to the present invention may be remote from or in closeproximity to a process tool that is to utilize air processed by thesystem. In accordance with such embodiments, while some elements may belocated in close proximity to the process tool, other elements may beremote from the process tool. Along these lines, a first desiccant dryerincluded in a system according to the present invention may be locatedremote from a process tool that utilizes air cooled and dried by thesystem while a second desiccant dryer may be arranged in close proximityto the process tool.

According to some embodiments, the present invention also includes adistribution system for distrusting air cooled and dried by the systemfrom the first air cooling unit or other element of the system to aplurality of process tools.

To encourage flow of air through a system according to the presentinvention, the present invention may include at least one fan. The atleast one fan for directing and encouraging air flow through the systemmay be arranged in a plurality of positions. For example, the at leastone fan could be located at an inlet of the system. The at least one fancould also be located at an outlet of the system downstream from an aircooling unit or desiccant dryer. According to an embodiment where atleast one fan is arranged in the vicinity of an outlet of the system,the at least one fan could be located in the vicinity of the coolingunit or desiccant dryer or in the vicinity of the process tool. The atleast one fan may also be located anywhere in the air flow path throughthe system.

The present invention may also include a plurality of fans. For example,a fan could be located at an inlet of the system while a second fancould be located in the vicinity of an outlet of the system. A fanlocated in the vicinity of an outlet of the system could be consideredan exhaust fan for discharging air from the system.

As described below in greater detail, a system according to the presentinvention may include more than one outlet. However, the presentinvention includes at least one outlet at a process tool. Although, thisoutlet may be connected to some sort of manifold to direct air at and/orthrough the process tool. Therefore, the “outlet” may not be an outletin a strict sense. However, a system according to the present inventionmay also include one or more outlets that vent air from the systementirely.

For further controlling and monitoring a system according to the presentinvention, the system may include at least one sensor for detectingcharacteristics of air flowing through the system. At least one sensormay be a temperature sensor. Alternatively, the at least one sensor maybe a humidity sensor. The humidity sensor could comprise wet and drybulb thermometers. Other types of sensors that could be included in asystem according to the present invention include dew point sensor(s),pressure sensor(s), and manual water flow sensors (s).

The present invention may also include more than one sensor. Forexample, a system according to the present invention may include atleast one temperature sensor and at least one humidity sensor.Naturally, the present invention may include any number of temperature,humidity, and/or other types of sensors.

The sensor or sensors may be arranged at any location within air flowpath in the system according to the present invention. For example, theat least one sensor could be arranged at the outlet of the system todetermine whether the air matches the desired parameters. A plurality ofsensors may also be arranged at various locations throughout the systemto monitor conditions at any desired point in the system.

To further monitor operation of a system according to the presentinvention, the system may include at least one sampling line forsampling air flowing through the system. The at least one sampling linemay be located at any location in the system. For example, at least onesampling line could be located at the exit of the system to sample theair exiting the system to determine whether it has the desiredcharacteristics of air treated by the system. The at least one samplingline could also be located at any other point in the system. Someembodiments may include a plurality of sampling lines to sample air atvarious locations throughout the system. Providing a sampling lineand/or at least one sensor downstream of any element of the system, suchas any desiccant dryer or any air cooling unit may help to more closelymonitor the performance of an individual element of the system.

According to some embodiments, a system according to the presentinvention may include at least one recycling line for recycling at leasta portion of the air flowing through the system. According to suchembodiments, air that is not able to be used by a process tool may berecycled through the system rather than being disposed of or vented. tothe atmosphere. This may help to save money as compared to a system notincluding at least one recycling line.

Typically, as with many other apparatuses utilized in semiconductordevice manufacturing, a system according to the present invention mayhave people working in the vicinity of the system. Accordingly, thepresent invention may include at least one sound attenuator forattenuated sound generated by the system. The sound attenuator may bearranged at any one or more locations in the system.

FIG. 1 schematically illustrates an embodiment of an air drying systemaccording to the present invention. This embodiment is shown anddescribed simply to provide one example of the present invention. Thisexample should be considered illustrative and not restrictive.

Air enters the embodiment of the system illustrated in FIG. 1 at inlet 1indicated by arrow 3. A system illustrated in FIG. 1 includes a coolingcoil 5 through which the air first flows. Air then flows along flow path7 to first desiccant dryer 9.

A regeneration exchange fan 11 may remove a portion of the air flowinginto the first dryer through outlet 13. Any fan may be utilized herewith any desired power. According to one embodiment, a fan having about3 horsepower may be utilized as fan 11.

Air removed from the first desiccant dryer may travel flow path 13toward a flat plate air to air heat recovery unit 15. Air may also flowinto the heat recovery unit from a regeneration air supply 17 and fromrecirculation or recycling lines 19 and 21 for recycling a portion ofthe air from elements of the system downstream of the desiccant dryer 9.

In the heat recovery unit, heat exchangers transfer heat from airflowing into the flat plate air to air heat recovery unit 15 from theflow paths 17, 19 and 21 into air flowing from the first desiccant dryer9 through flow path 13. Air input into the heat recovery unit 15 fromflow paths 17, 19 and 21 exits the heat recovery unit through flow path23 to flow back toward the first desiccant dryer 9. From flow path 17 toflow path 23, the air temperature may increase from about 72° F. toabout 114° F. dry bulb temperature.

Prior to entering the first desiccant dryer, the air may flow through aregeneration heater unit 25. The heater unit 25 may operate withelectric or gas or any other type of heat. According to one example, theheater unit 25 is electric and generates about 84 kilowatts of heat.

After flowing through the heat recovery unit 15, air that was removedfrom the first desiccant dryer through flow path 13 may flow out of theheat recovery unit through flow path 27 toward a regeneration coolingunit 29. Air flowing through the regeneration recooling unit 29 may exitthe unit through flow path 31. The cooling unit 29 recools the air andremoves moisture prior to releasing the air to the environment. This canhelp to reduce any environmental output from the process. In coldoutside conditions, removing moisture from the air prior to venting theair to the atmosphere can reduce formation of ice and/or snow as themoist air encounters the cold atmosphere. Such ice and/or snow couldbuild up and present a hazard.

The air may flow through flow path 31 toward regeneration air exhaustfans 33 and 35. Air may exit exhaust fans 33 and 35 as indicated byarrows 37 and 39. In an embodiment such as that illustrated in FIG. 1that includes two exhaust fans arranged as indicated in FIG. 1, one ofthe exhaust fans may be on-line while the other may be on standby. Thestandby fan could activate upon failure of the on-line fan.

Arranged in the flow path 31, upstream of each fan may be a motorizedback draft damper 41 and 43. The dampers may prevent air flow backthrough flow path 31 away from fans 33 and 35 toward the regenerationrecooling unit 29. The motorized back draft dampers may be wired suchthat they open upon starting of fans 33 and/or 35.

Also arranged in flow path 31 may be a barometric relief damper 45. Thebarometric relief damper may provide a pressure outlet in the event thatpressure exceeds a certain level.

Flow switches 47 and 49 may be arranged within the flow paths just priorto dampers 41 and 43. The flow switches indicate that air is flowingthrough the system at those locations. If desired, the flow switches canalert an operator in the event the air movement ceases.

As discussed above, air entering the heat recovery unit through flowpaths 17, 19 and 21 may be directed back toward the first desiccantdryer 9. This air and a portion of the air not removed by theregeneration exchange fan 11 may exit the first desiccant dryer 9through flow path 51.

As stated above, a system according to the present invention may includeat least one sampling line. The embodiment illustrated in FIG. 1includes two sampling lines 53 and 55. Sampling lines 53 and 55 mayremove a portion of the air flowing through flow path 51.

As also stated above, the present invention may include at least onesensor. For example, the embodiment illustrated in FIG. 1 includes a dewpoint indicator 57 arranged in the sampling lines 53 and 55.

A system according to the present invention may include at least onevalve to control flow of air through the system. For example, theembodiment illustrated in FIG. 1 includes valves 59, 61, and 63 tocontrol flow of air flowing through the sampling lines 53 and 55. As canbe seen in FIG. 1, air exiting flow path 51 through sampling lines 53may be returned to the flow path 51 through sampling line 55.

Flow path 51 leads from first desiccant dryer to cooling coil 65.Cooling coil 65 as cooling coil 5 serves to help cool the air flowingtherethrough. Any type of cooling unit may be utilized here. Accordingto one example, the cooling unit is a chilled water cooling unit.Additionally, the amount that the cooling unit 65 cools the air maydepend upon the input air and the desired output. According to oneexample, air input into the cooling unit 65 has a temperature of about99° F., dry bulb. According to this example, the cooing unit cools theair to a temperature of about 73° F., dry bulb. Air exits cooling coil65 through flow path 67.

At this point in the flow path, a fan 69 may be located to facilitatemovement of air through the system. The fan may be a high pressuresupply fan. While any fan could be utilized here, a fan having ahorsepower of about 15 could be utilized. The operational parameters ofthe fan may vary. According to one example, air exits the fan at a flowrate of about 3500 cubic feet per minute. According to this example, fanproduces a static pressure of about 10 inches, operates at a speed ofabout 1628 revolutions per minute, and has a brake horse power of about8.22. Air can exit this fan at a velocity of about 2823 feet per minute.Of course, as stated about with respect to the temperature and moisturecontent of the air, the fan operational parameters may vary. Air exitsthe fan 69 through flow path 71.

It is at this point in the flow path that a sound attenuator 73 may bearranged. Air may exit the sound attenuator through discharge plenum 75.

As indicated by flow path 79, a portion of the air may be discharged bythe discharge plenum toward the dew point indicator 57. A valve 81arranged in flow path 79 may permit this flow path to be opened andclosed. Valve 81 may operate in cooperation with valves 59 and 61 tocontrol which air is supplied to the dew point indicator. This maypermit the dew point of the air to be sampled at various locations inthe system.

At the point where the air is discharged from the discharge plenum, theflow path may split directed the air along two different flow paths 83and 85. Each flow path 83 and 85 may lead to a second desiccant dryerand cooling unit and to one or more process tools. Valves 87 and 89 maycontrol flow of air through the flow paths 83 and 85. Valves 87 and 89may be butterfly dampers.

Each flow path 83 and 85 may lead to a second cooling unit 91 and 93.The second cooling unit is located upstream and directly adjacent seconddesiccant dryers 95 and 97.

From the second cooling unit, the flow path in the embodimentillustrated in FIG. 1 leads into a second desiccant dryer 95 and 97.First cooling units 99 and 101 are arranged downstream from the seconddesiccant dryers 95 and 97, respectively. Air may flow from the seconddesiccant dryers to the first cooling units through flow paths 96 and98.

As indicated by flow paths 119 and 121, a portion of the air exiting thesecond desiccant dryers may not be directed through flow paths 96 and 98and eventually toward the process tools but rather flow through flowpaths 119 and 121 toward the heat recovery unit 15. Fans 123 and 125 mayhelp to direct the flow of air through flow paths 119 and 121.

The air may be redirected rather than discarding it. By supplyingpreviously dried air to dryer 9, this may also help to ensure that thedryer 9 can work less hard if desired as compared to if the dryer onlyreceived air through flow path 7. This could improve the reliability ofthe dryer as well as decreasing the heat required to run it.

Second cooling units 91 and 93 may chill the air utilizing chilledwater. On the other hand, first air cooling units 99 and 101 may chillthe air utilizing chilled water and/or refrigerant-based system. Therefrigerant system may utilized any typical refrigerant, such as freonor freon replacement compounds.

FIG. 2 illustrates one embodiment of a first air cooling unit along witha second desiccant drier and second cooling unit that may be utilizedaccording to the present invention. The embodiment illustrated in FIG. 2includes an inlet for receiving air from flow paths 83 and 85 from theparts of the system upstream in the flow paths from the first aircooling unit. Air entering the embodiment shown in FIG. 2 firstencounters second cooling unit 91/93. For clarity, reference numbersfrom FIG. 1 will be utilized whenever possible in the description of theportion of the system shown in FIG. 2.

In this embodiment, the second cooling unit 91/93 is a chilled watercooling coil. The first cooling coil receives chilled water from achilled water supply 107/109. The chilled water may come from anexisting chilled water supply in any manufacturing facility.

As indicated by broken line 111/113, the chilled water may be directedto other cooling coils in the first air cooling unit. According to oneembodiment, air entering the first second cooling unit 91/93 has atemperature of about 75° F., a moisture content of about 5 to about 6grains and a flow rate of about 1540 SCFM. After exiting the firstcooling coil, the air may have a temperature of about 54° F.

As stated above, the properties of the air entering the system andoperational requirements may vary the characteristics of the air at anypoint within the system. Also, importantly, the flow rates providedherein represent values in standard cubic feet per minute. If the air isnot at standard temperature and pressure, these values will differ.

After leaving the second cooling unit 91/93, the air will travel tosecond desiccant dryer 95/97. Second desiccant dryer 95/97 can operateas any desiccant dryer described herein. The second desiccant dryer inthe embodiment illustrated in FIG. 2 can reduce the moisture content ofthe air to less than about 1 grain. In one particular embodiment, themoisture content is reduces to about 0.073 grain. The air can exit thesecond desiccant dryer at a temperature of about 66.8° F. and at a flowrate of about 1200 SCFM. This portion of the air discharged throughsecond desiccant dryer may exit through flow path 96/98.

A reactivation heater access panel 141 may be arranged adjacent thesecond desiccant dryer.

Part of the air entering second desiccant dryer 95/97 will exit throughflow path 19/21 to be recirculated back to a heat recovery unit asdiscussed above. Flow of air may be facilitated by fan 123/125. Thisrecycled air, or reactivation discharge air, may have a temperature ofabout 140° F., a moisture content of about 22.3 grains and a flow rateof about 340 SCFM. Unlike the embodiment illustrated in FIG. 1, wherethe reactivation discharge air is shown splitting off from flow paths 96and 98 after the desiccant dryer, the reactivation discharge air in theembodiment illustrated in FIG. 2 exits directly from the seconddesiccant dryer.

Air exiting the second desiccant dryer through flow path 96/98 passesinto first air cooling unit 99/101. The embodiment of the first aircooling unit shown in FIG. 2 utilizes four cooling coils. The coolingcoils in the first air cooling unit can rely on any type of cooling. Forexample, the cooling coils can be chilled water or conventionalrefrigerant based cooling coils. In the embodiment represented in FIG.2, one of the cooling coils is a chilled water while three of are directexpansion cooling coils.

Air flows from flow path 96/98 into a first cooling coil 147. This firstcooling coil, labeled coil #1 in FIG. 2, is a chilled water coolingcoil. According to one embodiment, cooling coil 147 outputs air have atemperature of about 55° F., a moisture content of about 0.073 grains,and a flow rate of about 1200 SCFM.

Air exiting cooling coil 147 then flows to cooling coil 149. Coolingcoil 149 can chill the air to about −3° F., while not altering itsmoisture content or flow rate. This cooling coil is labeled as coolingcoil #2 in FIG. 2. Unlike cooling coil 147, cooling coil 149, in theembodiment shown in FIG. 2 is a direct expansion cooling coil.

The embodiment of first air cooling unit 99/101 illustrated in FIG. 2includes two more cooling coils, 151 and 153. These cooling coils arelabeled as coils 3 and 4, respectively, in FIG. 2. Similar to coolingcoil 149, cooling coils 151 and 153 are direct expansion cooling coilsin the embodiment illustrated in FIG. 2. Air exiting cooling coil 151may have a temperature of about −30° F., with the same flow and moisturecontent of air exiting cooling coil 149. Air may then flow to coolingcoil 153. Air exiting cooling coil 153 may have a temperature ofapproximately −39° F., again, with the same flow and moisture content ofair exiting cooling coils 151 and 149. Air exits the first air coolingunit at output 103/105.

The first air cooling unit represented in FIG. 2 also includescondensers 157, 159, and 161 for cooling the refrigerant prior tointroducing the refrigerant into direct expansion cooling coils 149,151, and 153. After exiting the condenser 161 for direct expansioncooling coil 153, the chilled water may be returned to the systemthrough exits/flow paths 115 and 117.

By utilizing chilled water in the cooling units, an. existing chilledwater producer may be utilized in a system according to the presentinvention. Chilled water may enter the second cooling units throughcooling water inputs 107 and 109. The cooling water may exit the secondcooling units and flow toward the first cooling units through flow paths111 and 113. The chilled water may exit the first cooling units throughexits/flowpaths 115 and 117.

Air exits the system through exit flow path 103 and 105. By includingmore than one flow path out of the discharge plenum and eventual outletfrom the system, a system according to the present invention may producemore than one flow of supply air having more than one characteristic. Inother words, air flowing from the first cooling unit 99 may havedifferent properties than air flowing from the first cooling unit 101.

While air may flow through a system according to the present inventionat any desired rate and the temperature and humidity may be controlledat any desired degree, the following provides an example of air flowingthrough the system illustrated in FIG. 1, providing flow rates andmoisture contents and dew point measurements. Along these lines, air maybe input into the system at input 1 at a maximum rate of about 3,080cubic feet per minute. According to one example, the air input into thesystem has a dry bulb temperature of about 75° F. and a wet bulbtemperature of about 63° F. The air may have a moisture content of about68 grains.

The air exiting the cooling coil through flow path 7 may have a dry bulbtemperature of about 47° F. and a wet bulb temperature of about 46.9° F.This air may have a moisture content of about 47 grains. The firstdesiccant dryer 9 may have a flow capacity of about 4500 cubic feet perminute.

Air removed from the first desiccant dryer by the regeneration exchangefan 11 may be removed from the first desiccant dryer at a rate of about1,035 cubic feet per minute. The air flowing through the fan may have adry bulb temperature of about 120° F. and have a moisture content ofabout 169 grains. Air flowing through flow path 31 toward exhaust fan 33and 35 may have a dry bulb temperature of about 71° F. and a wet bulbtemperature of about 69° F.

Air flowing into the heat recovery unit 15 from regeneration air supply17 may flow at a rate of about 355 cubic feet per minute. This air mayhave a dry bulb temperature of about 75° F. and a moisture content ofabout 68 grains. On the other hand, air flowing into the heat recoveryunit 15 that has been recycled from the second desiccant dryers throughflow lines 19 and 21 may flow at a rate of about 340 cubic feet perminute. This air may have a temperature of about 140° F. (or 60° C.) anda moisture content of about 23 grains per pound.

Air flowing out of the heat recovery unit 15 toward the first desiccantdryer may flow at a rate of about 1,035 cubic feet per minute and have adry bulb temperature of about 114° F. This air may have a moisturecontent of about 40 grains.

Air flowing through flow path 51 from first desiccant dryer to coolingcoils 65 may have a dry bulb temperature of about 99° F. and a wet bulbtemperature of about 67° F. This air may have a moisture content ofabout 4.5 grains.

After leaving a cooling coil 65 and entering flow path 67, the air mayflow at a rate of about 3080 cubic feet per minute. This air may have adry bulb temperature of about 73° F. and a wet bulb temperature of about47° F. This air may have a moisture content of about 4.5 grains.

Air exiting the discharge plenum 75 of the vertical sound attenuator 73may flow through flow paths 83 and 85 at a rate of about 1540 cubic feetper minute. This air may have a dry bulb temperature of about 75° F. anda moisture content of about 4.5 grains. Of course, air may flow throughflow pass 83 and 85 at different rates.

Air exiting the system toward process tools through flow paths 103 and105 may have a temperature of approximately −39° C. The flow ratethrough these flow paths may be about 1200 standard cubic feet perminute to feed air to 16 tools each requiring a flow of about 70 SCFM.Of course, the flow rate may vary, depending at least in part on theheat gain from the particular tools that the air is being supplied to.Other embodiments could have flow rates greater or lesser than 1200SCFM. For example, the flow rate could be 2400 SCFM or 3400 SCFM. Airflowing through flow paths 96 and 98 from second desiccant dryers 95 and97 to first cooling units 99 and 101 may flow at a rate of about 1200cubic feet per minute.

As discussed above, the present invention also provides methods forcooling and drying air. The methods include transmitting air through asystem such as that described above. The methods may alternatively oradditionally be considered to include drying the air and cooling the airsuch that it has the desired moisture and temperature characteristics.The drying and cooling may take place in more than one stage.

The present invention also includes methods for testing a semiconductordevice. Similar to the methods of cooling and drying air, the methodsfor testing a semiconductor device may include arranging a semiconductordevice and in or on a testing apparatus and transmitting air through asystem according to the present invention and then directing the air tothe testing device to cool the semiconductor device and carrying out thetesting of the semiconductor device. Alternatively and/or additionally,methods for testing a semiconductor device according to the presentinvention may include drying and cooling the air such that it hascharacteristics discussed above. The air may then be directed to thetesting device and the semiconductor device tested.

As indicated in FIG. 1, some moisture may be removed by the firstdesiccant dryer. The air may then be shipped at room temperature toseveral process areas rather than being cooled down. When arriving inclose proximity to the process areas, the air may be cooled and driedmore. Along these lines, the air may be cooled by the second coolingunit to about 20° C. The second desiccant dryer may then dry it furtherand the first cooling unit may further chill it down to about −39° C.The air may then be distributed through duct port to several tools.According to one embodiment, a system such as that illustrated in FIG. 1provides air to at least 16 testing apparatuses. Of course, more or lesstest apparatuses could be supplied with air from the system.

At least some embodiments of the present invention may be considered tocomprise a split desiccant air conditioning system that combine producescold air at subfreezing temperatures, down to about −39° C. andtransmits this air through a duct system to individual testerseconomically and without coil freeze up. The desiccant dryer(s) mayinclude rotating honeycomb wheels utilizing silica gels as an absorbent.Another absorbent that could be utilized is lithium chloride.

The desiccant dryers can include a heater that removes moisture from theair. Such heaters, often referred to as reactivation heaters could beelectric, steam, indirect-fired gas, or direct-fired gas. However,lithium chloride typically cannot be utilized in a dehumidifier thatuses direct-fired gas reactivation. The wheel in such an apparatus couldbe damaged.

The final cooling of the air supply may be achieved utilizing aself-contained air handling unit. As discussed above, an existingchilled water system may be utilized for condensation purposes.Refrigerant compressors may also be utilized coupled with a directexpansion coil for the final cooling. The air cooling system equipmentaccording to the present invention may create a constant volume system.

As discussed above, a relief duct may be included in a system accordingto the present invention. The relief duct is not shown in FIG. 1.However, it is arranged downstream of any testing tools supplied withair by the system. According to one example, a relief duct is arrangedunder a floor, such as a raised floor typically utilized in computerinstallations. The chilled air could, when supplied through a reliefduct, supplement or replace, at least temporarily, the air conditioningsystem typically necessary to cool the computer installation. Air couldalso be redirected back to the input of the entire system at flow path3.

An advantage of a system according to the present invention is that itcan operate 24 hours per day, 7 days a week. This is at least in partdue to the lack of problems associated with liquid nitrogen chillersdiscussed above. As a result, the relief duct described above can bevery useful, especially to avoid wasting the chilled air.

The foregoing description of the invention illustrates and describes thepresent invention. Additionally, the disclosure shows and describes onlythe preferred embodiments of the invention, but as aforementioned, it isto be understood that the invention is capable of use in various othercombinations, modifications, and environments and is capable of changesor modifications within the scope of the inventive concept as expressedherein, commensurate with the above teachings, and/or the skill orknowledge of the relevant art. The embodiments described hereinabove arefurther intended to explain best modes known of practicing the inventionand to enable others skilled in the art to utilize the invention insuch, or other, embodiments and with the various modifications requiredby the particular applications or uses of the invention. Accordingly,the description is not intended to limit the invention to the formdisclosed herein. Also, it is intended that the appended claims beconstrued to include alternative embodiments.

What is claimed is:
 1. An air cooling system, comprising: a firstdesiccant dryer; a second desiccant dryer connected in series in a flowpath with the first desiccant dryer wherein air flowing out of thesecond desiccant dryer has a moisture content of less than 1 grain; afist air cooling unit connected in series in the flow path with thesecond desiccant dryer; and a device for testing an electronic componentwherein air cooled and dried by the system is directed to said device.2. The system according to claim 1, further comprising a second aircooling unit in series in the flow path between the first desiccantdryer and the second desiccant dryer.
 3. The system according to claim2, wherein the second air cooling unit is dehumidifying.
 4. The systemaccording to claim 1, wherein the second desiccant dryer is arranged ontop of the first air cooling unit.
 5. The system according to claim 1,wherein the first air cooling unit is multi-stage.
 6. The systemaccording to claim 5, wherein the first air cooling unit comprises achilled water cooling coil and multiple stages of direct expansioncoils.
 7. The system according to claim 1, wherein the first air coolingunit comprises a chilled water cooling coil.
 8. A method for cooling anddrying air, the method comprising: drying the air such that it comprisesabout 4.5 grains of moisture; cooling the air to about 73° F.; andfurther cooling and drying the air such that the air comprises less thanabout 4.5 grains of moisture and is at a temperature of about −39° C. bypassing the air over cooling fins cooled by a non-nitrogen basedcoolant.
 9. A method for testing a semiconductor device, the methodcomprising: arranging the semiconductor device in a testing apparatus;drying air such that it comprises about 4.5 grains of moisture; coolingthe air to about 73° F.; further cooling and drying the air such thatthe air comprises less than about 4.5 grains of moisture and is at atemperature of about −39° C. by passing the air over cooling fins cooledby a non-nitrogen based coolant; and directing the air to the testingdevice to cool the semiconductor device.